1. Field of the Invention
The present invention relates to methods of thermal processing of carbonaceous feedstock materials containing vanadium, such as petroleum vacuum residuum, petroleum coke, kerogen from oil shale, and bituminous sand, e.g., tar sand or oil sand, or extra heavy oil, as well as carbonaceous ash, soot, or other residue resulting from the incomplete oxidation of these materials, for the purpose of concentrating vanadium and other metal compounds.
2. Description of the Prior Art
Carbonaceous materials that contain significant concentrations of vanadium, apart from their hydrocarbon content, pose significant problems when thermally processed in the presence of oxygen (either as elemental oxygen vapor or as contained in oxides like water vapor or hydrogen peroxide). Typical examples of these carbonaceous materials include petroleum vacuum residuum, petroleum coke, kerogen from oil shale, and bituminous sand e.g., tar sand or oil sand, or extra heavy oil, as well as carbonaceous ash or soot resulting from the incomplete combustion of these materials.
The problems due to thermal processing with oxygen stem from the wide range of melting points exhibited by the oxides of vanadium (ranging from about 1240° F. to 3580° F. for the vanadium-oxygen system alone) depending on the oxidation state, and the detrimental effects of vanadium slags on most refractory materials. Furthermore, depending on the other elements concentrated along with the vanadium in the residue, eutectic mixtures with even lower melting points can form (especially with alkali materials), yielding extremely low-viscosity and highly corrosive slags that may be accompanied by lumps or agglomerates of the higher-melting point, non-eutectic residual material.
Despite the difficulties exhibited by thermal processing of the aforementioned materials, thermal processing of these materials remains the predominant method for concentrating the vanadium since other techniques, such as floatation, extraction, or size classification, are largely irrelevant for these materials due to the vanadium being well dispersed in the organic phases and chemically complexed within porphyrin-like structures where elemental vanadium, vanadium oxides, or vanadium ions cannot be physically separated nor easily chemically extracted from the organic phase. Further sequestration of the vanadium in these materials (especially petroleum coke and some kerogens) is accomplished by the containment of these vanadium-porphyrin complexes within a dense matrix of polycyclic hydrocarbons which can make physical separation or chemical extraction almost impossible. Further advantages of the thermal processing with oxygen over physical separation or chemical extraction are the potential to produce a synthesis gas or by extracting thermal energy from the products of combustion in the same apparatus that accomplishes the concentration. In fact, the value of the synthesis gas or thermal energy typically exceeds the value of the contained vanadium. As a result, most of the processes are designed with the concentration or recovery of vanadium as a secondary concern to the overall economics of the process. Regardless of process economics based on vanadium or energy content, the process must still contend with the slagging and corrosion characteristics of the vanadium species in these residues.
It is apparent from the substantial body of prior art associated with the thermal processing of vanadium-containing, carbonaceous materials, that it has historically been a challenge to process these materials. If the vanadium content in the residue, ash, or soot is sufficiently high, it may be economically feasible to recover the vanadium from these residual materials. It is important that slagging and corrosive nature of these materials be mitigated if economical recovery of vanadium is to be achieved in a practical process.
A majority of the prior art techniques for the recovery of vanadium from residual waste use slagging gasification, hydrometallurgical, molten metal, molten salt, and roasting-hydrometallurgical processing techniques. Because of the challenges associated with vanadium containing slags, a limited number of technology suppliers offer processes for the direct combustion of petroleum coke residues/ashes/soots. Prior art related to the recovery of vanadium from these materials is summarized hereinafter.
The slagging gasifier developed by Texaco Inc. is a high temperature gasification process for the processing of petroleum coke (see, for example, U.S. Pat. Nos. 4,952,380; 4,826,627; 4,801,402; 4,708,819; 4,705,536; 4,668,428; 4,657,702; and 4,654,164). The primary purpose of this gasifier is to produce a synthesis gas from petroleum coke for use in the refining operations. It includes a number of techniques associated with coping with the slagging nature of the vanadium and nickel compounds found in the residuals of petroleum cokes. Under gasification conditions, the vanadium compounds exist primarily as suboxides. The suboxides of vanadium are refractory-like in nature and have high melting points. This, in turn, requires that the gasifier operate at elevated temperatures, which can lead to operational problems and decreases refractory life. This slagging gasification technology uses additives or fluxes to reduce the slagging temperature of the resultant residue to avoid clumping and agglomeration of the slag material so as to allow the effective removal of the slag from the gasifier. The slag removed from the gasifier may contain elevated levels of vanadium which can be further beneficiated using hydrometallurgical techniques.
Marathon Ashland Petroleum LLC discloses a molten metal bath to dissolve the carbon, sulfur, vanadium and nickel in petroleum coke in a molten metal bath (see, for example, U.S. Pat. Nos. 6,284,214; 6,241,803; 6,235,253; and 6,231,640). Oxygen is added to the bath to oxidize the carbon, and reducing gases are added to release the dissolved sulfur as H2S. The vanadium is recovered in a molten slag layer or as dust carried over in the flue gas effluent.
U.S. Pat. Nos. 4,389,378 and 4,536,374 disclose heating petroleum cokes to temperatures of about 1600° F. in the presence of metal sulfates and carbonates followed by hydrometallurgical leaching for the recovery of the vanadium.
U.S. Pat. No. 4,203,759 to Metrailer et al. discloses heating of petroleum coke in a fixed bed or moving bed reactor at a temperature less than 1050° F. so as to avoid the slagging and agglomeration of the contained metal oxides.
U.S. Pat. No. 4,443,415 discloses the processing of petroleum coke in the form of a slurry with an aqueous solution of sodium carbonate in a pressurized autoclave under oxidizing conditions and at moderate temperatures (about 600° F.) to produce a water leachable sodium vanadate that can be separated from the digestion residue.
U.S. Pat. No. 4,645,651 discloses the mixing of a petroleum residue with sodium carbonate and sodium sulfate, heating the mixture to the melting temperature of the mixture, treating the melt material with an aqueous phase and precipitating ammonium polyvanadate, sodium ammonium vanadate or ammonium metavanadate.
U.S. Pat. No. 4,243,639 discloses the gasification of petroleum coke with steam at temperatures in the range of about 1000° F. to 1500° F. in the presence of an alkali metal salt to produce a combustible gas and an inorganic ash containing a water soluble alkali metal vanadate.
U.S. Pat. Nos. 3,196,617 and 4,420,464 disclose the processing of carbonaceous materials in a molten alkali salt bath for the production of a low BTU synthesis gas. The residue may contain water-soluble vanadium compounds.
U.S. Pat. No. 3,873,669 discloses a hydrometallurgical process that involves the treatment of fly ash with a caustic soda solution to solubilize the vanadium contained in the fly ash. The process involves the subsequent treatment with lime, filtering/washing, vaporization and caustic treatment for recovery of the vanadium precipitate.
U.S. Pat. No. 5,772,726 discloses the use of an electric arc furnace with an iron bath to process vanadium containing ash with the addition aluminum as a reductant for the production of a ferrovanadium metal.
U.S. Pat. No. 5,277,795 discloses the combustion of petroleum coke in a slagging cyclone combustor at temperatures up to 2550° F., collecting the molten ash and recovering the metal compounds from the ash. This process is laden with the problems of slagging operation and the associated refractory and metal corrosion of V2O5 containing slags.
U.S. Pat. No. 5,427,603 discloses a process whereby a vanadium residue is heated to a temperature up to about 1560° F. under substoichiometric conditions with minimum oxygen partial pressure of 10−4 bar and a maximum oxygen partial of 10−2 bar, as measured within the region which is occupied by the residue. The patent discloses operation with a multiple hearth furnace, rotary kiln or fluidized bed reactor.
U.S. Pat. No. 6,193,941 discloses a process for producing a synthesis gas from an oil containing heavy metals by partially oxidizing the oil, recovering the soot formed, and subsequently burning the recovered soot in a pulverized fuel burner with a maximum operating temperature of about 1800° F. and an oxygen content above 1% while maintaining a reaction time of at most three seconds. The gas is then cooled to about 850° F. to 1200° F., prior to delivery to a waste heat recovery system and subsequent recovery of the vanadium-rich product.
Despite the foregoing, known methods, there remains a very real and substantial need for a method of thermal processing of carbonaceous materials containing vanadium in order to effect concentration of the vanadium.